Efficacy of Long-Acting Formulations of Estradiol or Progesterone Plus Estradiol on Estrous Synchronization in Broodmares Academic Article uri icon


  • A preliminary trial was performed to evaluate the ability of sustained release preparations of estradiol-17 or progesterone plus estradiol-17 to synchronize estrus in cyclic mares. Group 1 mares were treated with a 50 mg intramuscular (IM) injection of sustained release estradiol-17, while group 2 mares were treated with estradiol plus 1.5 g of sustained release progesterone. All mares received an IM injection of 10 mg of prostaglandin-F2 (PGF2) 10 days after steroid treatment. Mares were examined by transrectal ultrasonography on Days 1 and 10 of treatment and then at 2 day intervals to monitor follicle size. Once a follicle 30 mm diameter and uterine edema were detected, 0.5 mg of the GnRH analog histrelin was administered IM. Mares were examined daily thereafter to detect ovulation. Group 1 mares did not exhibit ovulation synchrony (ovulations occurred 12-22 days after steroid treatment), whereas ovulation synchrony was satisfactory in group 2 mares (interval to ovulation being 20.41.5 days, range 17-22 days). Using sustained release preparations of progesterone plus estradiol-17, with PGF2 administered on Day 10, could eliminate the need for daily injections of steroid preparations in oil when synchronizing estrus and ovulation. 2013 Elsevier Inc.

published proceedings


author list (cited authors)

  • Sudderth, A. K., Kiser, A. M., Brinsko, S. P., Love, C. C., Varner, D. D., Burns, P. J., & Blanchard, T. L.

citation count

  • 1

complete list of authors

  • Sudderth, A Kendrick||Kiser, Allison M||Brinsko, Steven P||Love, Charles C||Varner, Dickson D||Burns, Patrick J||Blanchard, Terry L

publication date

  • January 2013